The present invention relates to a fluid dispenser pump.
Fluid dispenser pumps are well known from the state of the art. Such a pump generally comprises a pump body which defines a pump chamber disposed between an inlet valve and an outlet valve, with a piston sliding in said pump body to deliver fluid contained in said pump chamber. In certain cases, the pump can have two pistons, namely an upper piston and a lower piston, which pistons slide together in the pump body while it is being actuated, until the outlet valve opens and the fluid contained in the pump chamber is delivered.
In certain cases, in particular with pharmaceuticals, dose-metering accuracy and guaranteed dispensing of a full dose each time the pump is actuated can be essential criteria. In particular, it is important to prevent incomplete doses from being dispensed, and to prevent the pump chamber from being filled in part only after said pump has been actuated.
An object of the present invention is to provide a fluid dispenser pump that guarantees dose-metering accuracy each time the pump is actuated, and that guarantees a full dose is dispensed.
Another object of the present invention is to provide such a fluid dispensing pump that is simple and inexpensive to manufacture and to assemble.
To these ends, the present invention provides a fluid dispenser pump comprising a pump body containing a pump chamber defined between an upper piston and a lower piston, said pistons being mounted to slide in leaktight manner in said pump body, said pump chamber being provided with an inlet valve and with an outlet valve, said lower piston co-operating with said outlet valve, when a full dose has been metered out, to open said outlet valve and to make it possible to deliver the fluid contained in the pump chamber, said dispenser pump being characterized in that the lower piston is separate from the inlet valve seat and is mounted to float in the pump chamber, said lower piston being returned to its rest position by said inlet valve seat.
Advantageously, the outlet valve comprises a valve member which is mounted to move in the pump chamber and which is urged into its closure position by pressure from the fluid contained in the pump chamber, said moving valve member being provided with a shoulder which, when a full dose has been metered out, co-operates with said lower piston or with an element integral therewith, so that the lower piston lifts the valve member off its valve seat so as to open the outlet valve.
Advantageously, the outside diameter of the upper piston is larger than the outside diameter of the lower piston.
Advantageously, the valve seat of the inlet valve is urged by a resilient element such as a spring into the rest position of the pump, in which position said lower piston or an element integral therewith urges the outlet valve into its closure position.
Advantageously, the lower piston acts as a primer element for removing the air contained in the pump chamber when the pump is actuated for the first time.
Advantageously, when the pump chamber contains air, an air removal passageway is formed between the lower piston, the upper piston and the inlet valve seat so as to enable the air to be removed from the pump chamber, said lower piston closing off said air passageway in leaktight manner when the pump chamber contains fluid to be dispensed.
Advantageously, the outlet valve member is provided with a second shoulder which co-operates with said lower piston or with an element integral with said lower piston, when the pump is in the rest position, so that the lower piston urges said moving valve member into its closure position.